Ive posted in the musical section, but thought it may be worth me posting here.

I have a valve guitar amp, as well as a pedal effects box also using a valve within it. seperately they both sound amazing but together they sound awful.

I am a qualified electrical eng but i have to say that valves ceased to be mainstream HIFI before i was born so i know little about them. I belive the issue im having is one of impedance-matching the headphone/line level output to the guitar(high impedance?) input of the amp.

anyone have any advice out there?

also, can anyone tell me how to gauge whether i need to replace my output valves(or indeed any of the preamp ones either)

**before anyone says it...i work with 33Kv on a daily basis, so i understand safe c.o.d's and have no qualms with SAFELY tinkering around inside my powered up amp-only if necessary**

I belive the issue im having is one of impedance-matching the headphone/line level output to the guitar(high impedance?) input of the amp

anyone have any advice out there?

What does "awful" mean? No bass? No treble? Distortion? Generally, a line or headphone output should be reasonably low Z, and the input to the amp should be high Z, which is just what you want. So, knowing what awful means, and perhaps knowing what the effects box and amp are, would be helpful.

Quote:

also, can anyone tell me how to gauge whether i need to replace my output valves(or indeed any of the preamp ones either)

Thats unusual. The pedal output should be low impedance and the amp in high, which shouldnt be a problem. A guitar straight in to a line level input is another thing and in the studio you use a DI box (direct input ) to match impedances. Does the pedal documentation state an output impedance? What does the pedal do? Is it just a matter of too much distortion from both pedal and amp?

Impedance seen by pedal too high
DC from pedal upsets tube bias
Voltage out from pedal too high

Solutions:

Pull-up resistor in hot lead
Cap in hot lead
Volume control

Combined:
Volume control with cap between signal in and pot. Pot value sets input impedance in parallel with Rgk, likely 470k to 1M for most guitar amps. Use wiper for signal out. Cap value sets low frequency roll-off in conjunction with input impedance, select for tone.